Reducing radicals in nitrate solutions. The NO32- system revisited

The one-electron reduction product of nitrate, the NO32- radical, was reinv estigated because of the contemporary interest in its reactivity in high-le vel liquid radioactive systems, Indirect observations suggest that the same dianion is produced by the precursor to the solvated electron. The redox p otential of the couple NO3-/NO32- was calculated, using several ab initio a pproaches combined with semiempirical solvation models, to be E-o approxima te to --1.1 V vs NHE. Using the theoretical prediction to guide the experim ent, we find a value of E-o = -0.89 V at zero ionic strength. Kinetic and f ree-energy-relationship arguments are used to question the acid-base equili bria and reaction mode that converts the NO32- to the oxidizing NO2 radical . It is proposed that the reaction of the dianion with various general acid s is an O2- (i.e., water or OH-) transfer to the acid and not proton transf er to NO32-, Implications of the highly negative redox potential of the dia nion and the existence of the protonated forms to practical systems are dis cussed.